classic PKU

[mjl1717]

Is tyrosine EVER at a normal level in classic PKU?

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[SomeDoc]

Levels should be low endogenously, unless the patient is on a tyrosine-fortified diet.

 

[mjl1717]

A 5-month-old infant is seen in the office for persistent vomiting, failure to thrive, and developmental
delay. His antenatal and postnatal histories are not available, as his Caucasian parents adopted him
when he was 4 months old. On physical examination, the infant appears blonde with fair skin and blue
eyes. You also notice a peculiar musty odor of the infant’s urine. Plasma phenylalanine level is 40mg/dl
and tyrosine levels are normal. There is also an increased urinary level of phenylpyruvic and o-hydroxy
phenylacetic acids. Which of the following is the etiology for this child’s symptoms?
A. Classic phenylketonuria
B. Benign hyperphenylalaninemia
C. Transient hyperphenylalaninemia
D. Tyrosinemia
E. Alcaptonuria

 

[xx216xx]

seems like classic PKU to me

"Babies with benign hyperphenylalaninemia or transient hyperphenylalaninemia usually have no symptoms at all."

http://www.drgreene.com/21_1156.html

 

[mjl1717]

seems like classic PKU to me

"Babies with benign hyperphenylalaninemia or transient hyperphenylalaninemia usually have no symptoms at all."

http://www.drgreene.com/21_1156.html

Thank you.. what gets me is that they say tyrosine level is normal?

 

[xx216xx]

well regardless of what they say about tyrosine levels, for a test you should pick the best answer and classic PKU is it from those options, it just can't be any of the others.

Couldn't tyrosine levels be normal if your intake of tyrosine is adequate? You could ingest phenlyalanine and tyrosine in the diet and have PKU symptoms with normal tyrosine levels, no? Biochem was a while back so I might be missing something.

 

[bodonid]

well regardless of what they say about tyrosine levels, for a test you should pick the best answer and classic PKU is it from those options, it just can't be any of the others.

Couldn't tyrosine levels be normal if your intake of tyrosine is adequate? You could ingest phenlyalanine and tyrosine in the diet and have PKU symptoms with normal tyrosine levels, no? Biochem was a while back so I might be missing something.

http://www.ncbi.nlm.nih.gov/pubmed/8942417?dopt=Abstract

wish me luck, Biochem NBME is wednesday!

 

[bodonid]

ignore the above, I think they were testing supplements, not the effects of a normal diet. But I looked around and it seems like (1) fasting tyrosine levels in pku are always low and (2) a high protein meal can elevate tyrosine to levels well above normal. So morning/fasting [tyr] would be a better predictor but its not always low.

 

[thechad]

I'm not sure, but I think the test for PKU is administered shortly after birth (a couple of weeks, right?). Why would they wait 5 months to test? Am I wrong?

 

[TMP-SMX]

I'm not sure, but I think the test for PKU is administered shortly after birth (a couple of weeks, right?). Why would they wait 5 months to test? Am I wrong?

If you aren't born in a hospital, you aren't getting newborn screening. In the past, only a few states even did newborn screening for PKU. Also, not all state screenings are created equal or even mandatory. Though every state now screens for PKU.

PKU is an important one to screen for as the devastating CNS effects are avoidable if it is recognized right away. Unlike many other congenital disorders, there is a treatment for it and it is important to know up front.

 

[bodonid]

plus, I know the PKU test is very sensitive, but I'm sure there are some false negatives. That and sample collection errors. I'm sure these people could come back at 5 months. You never know.

 

[mlw47]

A. Classic phenylketonuria
B. Benign hyperphenylalaninemia
C. Transient hyperphenylalaninemia
D. Tyrosinemia
E. Alcaptonuria

"Musty" or "mousy" odor are the buzz words for PKU.

Also, the reason why he's hypopigmented and has blue eyes is because he can't synthesize melanin since he has not enough tyrosine (which is, btw, is an essential AA).

 

[bodonid]

tyrosine isn't usually considered essential. it 'becomes' essential in pku, however.

 

[mlw47]

tyrosine isn't usually considered essential. it 'becomes' essential in pku, however.

Correct, my bad on being vague...

 

[bcat85]

Levels should be low endogenously, unless the patient is on a tyrosine-fortified diet.

This seems right to me.

 

[mjl1717]

Thank you guys for the quick replies!